Almond (Prunus dulcis (Mill.) D. A. Webb) is a traditional culture in Portugal, which gained a renewed interest due to the installation of new orchards. Grafting remains the main method used for almond propagation. The successful establishment of a graft union between two parts (scion and rootstock) requires auxins, which are involved in wound response and vascular regeneration. This work aimed at the quantification and immunolocalization of indole-3-acetic acid (IAA) in almond micrografts before micrografting (T0) and 21 days after micrografting (T2). The results are a step forward to understand of how auxin is involved in graft compatibility in almond.

In recent years, almond culture has increased in Portugal with the introduction of new orchards neglecting the traditional varieties. Micrografting, grafting in in vitro conditions, is a technique that has been established for commercial almond trees, but no studies have been described with Portuguese varieties. In this work, an efficient protocol for almond micrografting with traditional almond trees was established. The effect of plant growth regulators (BAP and IBA) and activated charcoal on culture medium were also evaluated during micrografting assays. Furthermore, the effect of auxin IBA on root induction was analysed during rooting assays.

Biscogniauxia mediterranea is the causal agent of charcoal disease in Quercus suber, the main species of the dynamic ecosystem, known as “Montado”, in the Alentejo region, Portugal. In the last years, almond orchards have been introduced in this region due to water availability through the Alqueva dam and the possibility of mechanical harvest. The high-density planting associated with mechanized harvesting and irrigation systems observed in these new orchards can potentiate the appearance of new diseases. In a survey conducted in March 2022, symptomatic diseased trees from Soleta and Vairo cultivars were detected in Beja, Portugal. From this material, we have isolated numerous cultures and could identify B. mediterranea from all individuals analyzed by molecular and morphological techniques. Pathogenicity tests were performed in almond plant material and successfully reisolated from lesions, confirming Koch’s postulates. Phylogenetics analyses demonstrated the similarity between our sequences and sequences from Quercus suber worldwide. To our knowledge, this is the first report of B. mediterranea causing diseases on almond trees (Prunus dulcis) in Portugal and worldwide.